Broadband 1.5-2.1 µm emission in gallo-germanate dual-core optical fiber co-doped with Er3+ and Yb3+/Tm3+/Ho3.

The near-infrared emission in fabricated low-phonon energy, gallo-germanate glass, and double-core optical fiber has been investigated. Broadband amplified spontaneous emission (ASE) was obtained in optical fiber with cores doped with: 1st - 0.2Er2O3 and 2nd - 0.5Yb2O3/0.4Tm2O3/0.05Ho2O3 as a result of the superposition of emission bands from both cores corresponding to the Er3+:4I13/2→4I15/2 (1st core) and Tm3+:3F4 → 3H6/Ho3+:5I7 → 5I8 (2nd core) transitions. The effect of fiber length and pump wavelength on the near-infrared amplified spontaneous emission (ASE) properties has been analyzed for 1 m and 5 m optical fiber. The widest emission bandwidth (355 nm - 3 dB level) was obtained for a 5 m length optical fiber pumped by a 940 nm laser.

Tellurite Glasses from the 70TeO2-5XO-10P2O5-10ZnO-5PbF2(X= Pb, Bi, Ti) System Doped Erbium Ions-The Influence of Erbium on the Structure and Physical Properties.

In this article, we present research on the influence of erbium ions on the structure and magneto-optical properties of 70TeO2-5XO-10P2O5-10ZnO-5PbF2 (X = Pb, Bi, Ti) tellurite glass systems. Structural changes occurring in the glasses during doping with erbium ions were investigated using positron annihilation lifetime spectroscopy (PALS) and Raman spectroscopy. The X-ray diffraction (XRD) method was used to confirm the amorphous structure of the investigated samples. Based on the Faraday effect measurements and calculated values of Verdet constant, the magneto-optical properties of the glasses were determined.

Luminescence Sensing Method for Degradation Analysis of Bioactive Glass Fibers.

The effects of Sm3+ content on the optical properties and bioactivity of 13-93 bioactive glass were presented. Sm3+ doped glass fibers drawn from bioactive glass were analyzed in simulated body fluid (SBF) for the determination of ion release. Optical analysis of the Sm3+ ions in bioactive glass fibers was used for degradation monitoring. While the fibers were immersed in SBF solution, changes in their luminescence spectra under 405 nm laser excitation were measured continuously for 48 h. The morphology of the fibers after the immersion process was determined by SEM/EDS. It was shown that the proposed approach to the analysis of changes in Sm3+ ion luminescence is a sensitive method for the monitoring of degradation processes and the formation of hydroxycarbonate-apatite (HCA) layers on glass fiber surfaces. SEM/EDS measurements showed a significant deterioration on the surface of the fibers and the formation of HCA on 13-93_02Sm bioactive glass. The optical analysis of the time constant indicated that bioactive glass fibers doped with 2 %mol Sm3+ degrade at a rate almost five times slower than 13-93_02Sm.

Fluoroindate Glass Co-Doped with Yb3+/Ho3+ as a 2.85 µm Luminescent Source for MID-IR Sensing.

This work reports on the fabrication and analysis of near-infrared and mid-infrared luminescence spectra and their decays in fluoroindate glasses co-doped with Yb3+/Ho3+. The attention has been paid to the analysis of the Yb3+→ Ho3+ energy transfer processed ions in fluoroindate glasses pumped by 976 nm laser diode. The most effective sensitization for 2 µm luminescence has been obtained in glass co-doped with 0.8YbF3/1.6HoF3. Further study in the mid-infrared spectral range (2.85 µm) showed that the maximum emission intensity has been obtained in fluoroindate glass co-doped with 0.1YbF3/1.4HoF3. The obtained efficiency of Yb3+→ Ho3+ energy transfer was calculated to be up to 61% (0.8YbF3/1.6HoF3), which confirms the possibility of obtaining an efficient glass or glass fiber infrared source for a MID-infrared (MID-IR) sensing application.

Influence of BaF2 and activator concentration on broadband near-infrared luminescence of Pr3+ ions in gallo-germanate glasses.

Thermal stability and broadband NIR luminescence of Pr(3+) doped gallo-germanate glasses with BaF2 have been studied. The thermal factors are larger for glass samples with low BaF2 content exhibiting good thermal stability against devitrification. Luminescence due to (1)D2 → (1)G4 transition of Pr(3+) was measured under 450 nm excitation. The (1)D2 measured lifetimes depend critically on activator concentration, but remain nearly unchanged with BaF2 content. The emission linewidth, the emission cross-section, the figure of merit (FOM) and the σem x FWHM product are relatively large, suggesting that Pr(3+)-doped gallo-germanate glasses with presence of BaF2 are promising as gain media for broadband near-infrared amplifiers.

Pr3+-doped YPO4 nanocrystal embedded into an optical fiber.

Optical fiber with YPO4:Pr3+ nanocrystals (NCs) is presented for the first time using the glass powder-NCs doping method. The method's advantage is separate preparation of NCs and glass to preserve luminescent and optical properties of NCs once they are incorporated into optical fiber. The YPO4:Pr3+ nanocrystals were synthesized by the co-precipitation and hydrothermal methods, optimized for size (< 100 nm), shape, Pr3+ ions concentration (0.2 mol%), and emission lifetime. The core glass was selected from the non-silica P2O5-containing system with refractive index (n = 1.788) close to the NCs (no = 1.657, ne = 1.838). Optical fiber was drawn by modified powder-in-tube method after pre-sintering of glass powder-YPO4:Pr3+ (wt 3%) mixture to form optical fiber preform. Luminescent properties of YPO4:Pr3+ and optical fiber showed their excellent agreement, including sharp Pr3+ emission at 600 nm (1D2-3H4) and 1D2 level lifetime (τ = 156 ± 5 µs) under 488 nm excitation. The distribution of the YPO4:Pr3+ NCs in optical fiber were analyzed by TEM-EDS in the core region (FIB-SEM-prepared). The successful usage of glass powder-NCs doping method was discussed in the aspect of promising properties of the first YPO4:Pr3+ doped optical fiber as a new way to develop active materials for lasing applications, among others.

Near-infrared to visible and ultraviolet upconversion in TiO2 thin films modified with Er and Yb.

Upconversion as a modification strategy to enhance the utilization of sunlight in titanium dioxide photoanodes with an internal upconverter was investigated. TiO2 thin films containing an Er activator and Yb sensitizer were deposited in the magnetron sputtering process on conducting glass, amorphous silica, and silicon. Scanning electron microscopy, energy dispersive spectroscopy, grazing incidence X-ray diffraction, and X-ray absorption spectroscopy allowed assessment of the thin film composition, structure, and microstructure. Optical and photoluminescence properties were measured by means of spectrophotometry and spectrofluorometry. Changing the content of Er3+ (1, 2, 10 at%) and Yb3+ (1, 10 at%) ions allowed us to achieve thin film upconverters with a crystallized and amorphous host. Upon 980 nm laser excitation Er3+ exhibits upconversion with the main emission in green (2H11/2 → 4I15/2, λ em ≈ 525 nm) and weak emission in red (4F9/2 → 4I15/2, λ em ≈ 660 nm). For a thin film with a higher ytterbium content (10 at%) a significant increase in red emission and upconversion from NIR to UV was observed. The average decay times of green emission for TiO2:Er and TiO2:Er,Yb thin films were calculated based on time-resolved emission measurements.

Analysis of Excitation Energy Transfer in LaPO4 Nanophosphors Co-Doped with Eu3+/Nd3+ and Eu3+/Nd3+/Yb3+ Ions.

Nanophosphors are widely used, especially in biological applications in the first and second biological windows. Currently, nanophosphors doped with lanthanide ions (Ln3+) are attracting much attention. However, doping the matrix with lanthanide ions is associated with a narrow luminescence bandwidth. This paper describes the structural and luminescence properties of co-doped LaPO4 nanophosphors, fabricated by the co-precipitation method. X-ray structural analysis, scanning electron microscope measurements with EDS analysis, and luminescence measurements (excitation 395 nm) of LaPO4:Eu3+/Nd3+ and LaPO4:Eu3+/Nd3+/Yb3+ nanophosphors were made and energy transfer between rare-earth ions was investigated. Tests performed confirmed the crystal structure of the produced phosphors and deposition of rare-earth ions in the structure of LaPO4 nanocrystals. In the range of the first biological window (650-950 nm), strong luminescence bands at the wavelengths of 687 nm and 698 nm (5D0 → 7F4:Eu3+) and 867 nm, 873 nm, 889 nm, 896 nm, and 907 nm (4F3/2 → 4I9/2:Nd3+) were observed. At 980 nm, 991 nm, 1033 nm (2F5/2 → 2F7/2:Yb3+) and 1048 nm, 1060 nm, 1073 nm, and 1080 nm (4F3/2 → 4I9/2:Nd3+), strong bands of luminescence were visible in the 950 nm-1100 nm range, demonstrating that energy transfer took place.

2-3 µm mid-infrared luminescence of Ho3+/Yb3+ co-doped chloride-modified fluorotellurite glass.

In this paper, Ho3+/Yb3+ co-doped chloride-modified fluorotellurite glasses with 2-3 µm mid-infrared luminescence are prepared. By measuring and investigating the transmission spectra and emission spectra, the prepared glasses show a high transmittance (91 %) and low maximum phonon energy (813 cm-1). Based on the measured absorption spectra, the Judd-Ofelt parameters and radiation characteristics were calculated in depth. In addition, with the assistance of phonons, the energy transfer between Ho3+/Yb3+ ions further increases the mid-infrared fluorescence intensity. The calculated emission cross-section at 2.0 µm and 2.85 µm reach 16.47 × 10-21 cm2 and 7.8 × 10-21 cm2, respectively. It is worth mentioning that the quantum efficiencies of Ho3+: 5I7→5I8 and 5I6→5I7 reach 51.47 % and 84.14 % respectively. The results having also in mind good thermal stability (ΔT = 102℃) and refractive index (n = 1.645) indicate that this glass has a promising application for the study of fiber lasers in the mid-infrared band.

Investigation of Thermal Sensing in Fluoroindate Yb3+/Er3+ Co-Doped Optical Fiber.

An investigation of fluoroindate glass and fiber co-doped with Yb3+/Er3+ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs-2H11/2 and 4S3/2), non-thermally coupled levels (non-TCLs-4F7/2 and 4F9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K-1-glass, 0.0019 K-1-glass fiber 2H11/2 → 4S3/2 transition) and relative sensitivity (2.05% K-1-glass, 1.64% K-1-glass fiber 4F7/2 → 4F9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications.

Tm3+/Ho3+ profiled co-doped core area optical fiber for emission in the range of 1.6-2.1 µm.

Double-clad optical fiber with a multi-ring core profile doped with thulium and holmium fabricated by Modified Chemical Vapor Deposition Chelate Doping Technology (MCVD-CDT) is presented. The measured Tm2O3 and Ho2O3 complexes' weight concentrations were 0.5% and 0.2% respectively. Numerical analyses show weakly guiding conditions and 42.2 µm of MFD LP01 at 2000 nm. The low NA numerical aperture (NA = 0.054) was obtained for the 20/250 µm core/cladding ratio optical fiber construction. The emission spectra in the range of 1.6-2.1 µm vs. the fiber length are presented. The full width at half maximum (FWHM) decreases from 318 to 270 nm for fiber lengths from 2 to 10 m. The presented fiber design is of interest for the development of new construction of optical fibers operating in the eye-safe spectral range.

Broadband Profiled Eye-Safe Emission of LMA Silica Fiber Doped with Tm3+/Ho3+ Ions.

LMA (Large Mode Area) optical fibers are presently under active investigation to explore their potential for generating laser action or broadband emission directly within the optical fiber structure. Additionally, a wide mode profile significantly reduces the power distribution density in the fiber cross-section, minimizing the power density, photodegradation, or thermal damage. Multi-stage deposition in the MCVD-CDT system was used to obtain the structural doping profile of the LMA fiber multi-ring core doped with Tm3+ and Tm3+/Ho3+ layer profiles. The low alumina content (Al2O3: 0.03wt%) results in low refractive index modification. The maximum concentrations of the lanthanide oxides were Tm2O3: 0.18wt % and Ho2O3: 0.15wt%. The double-clad construction of optical fiber with emission spectra in the eye-safe spectral range of (1.55-2.10 µm). The calculated LP01 Mode Field Diameter (MFD) was 69.7 µm (@ 2000 nm, and 1/e of maximum intensity), which confirms LMA fundamental mode guiding conditions. The FWHM and λmax vs. fiber length are presented and analyzed as a luminescence profile modification. The proposed structured optical fiber with a ring core can be used in new broadband optical radiation source designs.

Crystallization Mechanism and Optical Properties of Antimony-Germanate-Silicate Glass-Ceramic Doped with Europium Ions.

Glass-ceramic is semi-novel material with many applications, but it is still problematic in obtaining fibers. This paper aims to develop a new glass-ceramic material that is a compromise between crystallization, thermal stability, and optical properties required for optical fiber technology. This compromise is made possible by an alternative method with a controlled crystallization process and a suitable choice of the chemical composition of the core material. In this way, the annealing process is eliminated, and the core material adopts a glass-ceramic character with high transparency directly in the drawing process. In the experiment, low phonon antimony-germanate-silicate glass (SGS) doped with Eu3+ ions and different concentrations of P2O5 were fabricated. The glass material crystallized during the cooling process under conditions similar to the drawing processes'. Thermal stability (DSC), X-ray photo analysis (XRD), and spectroscopic were measured. Eu3+ ions were used as spectral probes to determine the effect of P2O5 on the asymmetry ratio for the selected transitions (5D0 → 7F1 and 5D0 → 7F2). From the measurements, it was observed that the material produced exhibited amorphous or glass-ceramic properties, strongly dependent on the nucleator concentration. In addition, the conducted study confirmed that europium ions co-form the EuPO4 structure during the cooling process from 730 °C to room temperature. Moreover, the asymmetry ratio was changed from over 4 to under 1. The result obtained confirms that the developed material has properties typical of transparent glass-ceramic while maintaining high thermal stability, which will enable the fabrication of fibers with the glass-ceramic core.

The Effect of Fluorides (BaF2, MgF2, AlF3) on Structural and Luminescent Properties of Er3+-Doped Gallo-Germanate Glass.

The effect of BaF2, MgF2, and AlF3 on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]4 and [GeO]6 units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF2. The 27Al MAS NMR spectrum of BGG glass with AlF3 suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the 4I13/2→4I15/2 transition of Er3+ ions increases in the BGG + MgF2 glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties.

Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering.

Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO2 and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO2 thin films containing erbium were deposited by radio frequency RF magnetron sputtering under ultrahigh vacuum conditions UHV. Morphology, structural, optical and electronic properties were studied. TiO2:Er thin films are homogenous, with uniform distribution of Er ions and high transparency over the visible VIS range of the light spectrum. However, a profound 0.4 eV blue shift of the fundamental absorption edge with respect to undoped TiO2 was observed, which can be attributed either to the size effect due to amorphization of TiO2 host or to the onset of precipitation of Er2Ti2O7 nanocrystals. Near-infrared NIR to VIS up-conversion is demonstrated upon excitation at 980 nm, while strong green photoluminescence at 525 and 550 nm occurs upon photon absorption at 488 nm.

Investigation of the TeO2/GeO2 Ratio on the Spectroscopic Properties of Eu3+-Doped Oxide Glasses for Optical Fiber Application.

This study presented an analysis of the TeO2/GeO2 molar ratio in an oxide glass system. A family of melt-quenched glasses with the range of 0-35 mol% of GeO2 has been characterized by using DSC, Raman, MIR, refractive index, PLE, PL spectra, and time-resolved spectral measurements. The increase in the content of germanium oxide caused an increase in the transition temperature but a decrease in the refractive index. The photoluminescence spectra of europium ions were examined under the excitation of 465 nm, corresponding to 7F0 → 5D2 transition. The PSB (phonon sidebands) analysis was carried out to determine the phonon energy of the glass hosts. It was reported that the red (5D0 → 7F2) to orange (5D0 → 7F1) fluorescence intensity ratio for Eu3+ ions decreased from 4.49 (Te0Ge) to 3.33 (Te15Ge) and showed a constant increase from 4.58 (Te20Ge) to 4.88 (Te35Ge). These optical features were explained in structural studies, especially changes in the coordination of [4]Ge to [6]Ge. The most extended lifetime was reported for the Eu3+ doped glass with the highest content of GeO2. This glass was successfully used for the drawing of optical fiber.

Structure and Luminescence Properties of Transparent Germanate Glass-Ceramics Co-Doped with Ni2+/Er3+ for Near-Infrared Optical Fiber Application.

An investigation of the structural and luminescent properties of the transparent germanate glass-ceramics co-doped with Ni2+/Er3+ for near-infrared optical fiber applications was presented. Modification of germanate glasses with 10-20 ZnO (mol.%) was focused to propose the additional heat treatment process controlled at 650 °C to obtain transparent glass-ceramics. The formation of 11 nm ZnGa2O4 nanocrystals was confirmed by the X-ray diffraction (XRD) method. It followed the glass network changes analyzed in detail (MIR-Mid Infrared spectroscopy) with an increasing heating time of precursor glass. The broadband 1000-1650 nm luminescence (λexc = 808 nm) was obtained as a result of Ni2+: 3T2(3F) → 3A2(3F) octahedral Ni2+ ions and Er3+: 4I13/2 → 4I15/2 radiative transitions and energy transfer from Ni2+ to Er3+ with the efficiency of 19%. Elaborated glass-nanocrystalline material is a very promising candidate for use as a core of broadband luminescence optical fibers.

Crystallization Kinetics and Structural Properties of the 45S5 Bioactive Glass and Glass-Ceramic Fiber Doped with Eu3.

An investigation of the crystallization kinetics of 45S5 Bioglass® using differential scanning calorimetry is presented in this paper. Thermal analysis was performed using the Friedman method. The activation energy and the Avrami index were calculated. The glass samples were subjected to additional controlled heat treatment at 620 °C in order to obtain bioactive glass-ceramics with enhanced mechanical properties. X-ray powder diffraction (XRD) measurements indicated the formation of the glass-ceramic structures of three cyclosilicates: Na4Ca4(Si6O18) or Na6Ca3(Si6O18) or Na16Ca4(Si12O36). Based on middle infrared region (MIR) results, it can be concluded that the crystalline phase present in the tested materials was Na6Ca3(Si6O18) (combeite). Material was doped with Eu3+ ions, which act as a spectroscopic probe for monitoring the structural changes in the glass matrix. The decreasing value of the fluorescence intensity radio parameter indicated symmetry around the europium ions and, thus, the arrangement of the glass structure. The bioactive properties of the examined glass-ceramics were also determined. The bioactive glass fibers doped with Eu3+ were manufactured using two different methods. Its structural and luminescent properties were examined.

Fluoroindate glasses co-doped with Pr3+/Er3+ for near-infrared luminescence applications.

Fluoroindate glasses co-doped with Pr3+/Er3+ ions were synthesized and their near-infrared luminescence properties have been examined under selective excitation wavelengths. For the Pr3+/Er3+ co-doped glass samples several radiative and nonradiative relaxation channels and their mechanisms are proposed under direct excitation of Pr3+ and/or Er3+. The energy transfer processes between Pr3+ and Er3+ ions in fluoroindate glasses were identified. In particular, broadband near-infrared luminescence (FWHM = 278 nm) associated to the 1G4 → 3H5 (Pr3+), 1D2 → 1G4 (Pr3+) and 4I13/2 → 4I15/2 (Er3+) transitions of rare earth ions in fluoroindate glass is successfully observed under direct excitation at 483 nm. Near-infrared luminescence spectra and their decays for glass samples co-doped with Pr3+/Er3+ are compared to the experimental results obtained for fluoroindate glasses singly doped with rare earth ions.

Optical emission spectroscopy of lead sulfide films plasma deposition.

In-situ Optical Emission Spectroscopy (OES) combined with quantum chemical calculations was used as a powerful tool to find out the exited reactive species existing in plasma discharge during the process of lead sulfide chalcogenide materials deposition. Low temperature nonequilibrium RF (40.68 MHz) plasma at low pressure (0.1 Torr) was employed for initiation of chemical interaction between precursors in the gas phase. Only high-pure elements were utilized as the initial substances. The ration between starting materials in the gas phase and power included into the plasma discharge were the variables. The mechanism of the plasma-chemical reaction was assumed and discussed. The stoichiometry and morphology of the surface of the as-deposited materials were studied by different analytical techniques.